Steve Coogan's appointment as a patron of Index on Censorship, has sparked a bitter row within the ranks of the free speech campaign group.

Private Eye editor Ian Hislop and his deputy Francis Wheen have quit as patrons - apparently in protest at Coogan's role in the Hacked Off campaign which led demands for tighter press regulation in the wake of the News of the World phone-hacking scandal.

Index chief executive Jodie Ginsberg has expressed "regret" at the resignations but defended the decision to appoint Coogan saying that freedom of speech depended upon open debate among people with differing opinions.

She said that the group continued to oppose the Royal Charter on press regulation backed by the three main political parties following the Leveson Inquiry findings and strongly supported by Coogan and Hacked Off.

However Wheen described Coogan's appointment as a "slap in the face", complaining that the comedian had no record of defending freedom of speech or a free press.

Index was originally established in 1972 during the Cold War with the backing of the poet Stephen Spender to highlight the plight of dissidents behind the Iron Curtain and has since established a record of defending free speech around the world.

It came out strongly against the Royal Charter, arguing that it introduced a layer of political control over the press that was "extremely undesirable", adding "our democracy is tarnished as a result".

Hislop, who is a regular panellist on TV's Have I Got News For You, was also among the fiercest critics of the Royal Charter regime, although other Index patrons, such as the playwright Sir Tom Stoppard have backed it.

Ginsberg said in a statement: "Our patrons are a diverse group of people, whose opinions sometimes diverge with our own. Free speech depends on open debate with people who may have points of view you disagree with.

"We regret that Ian and Francis have chosen to resign from our wide group of patrons. We have made it clear from the outset that we will not be changing our position on the Royal Charter.

"We will continue to maintain our focus on the work of those facing censorship in countries around the world, many who face daily threats of harassment, imprisonment and are at risk of being tortured or killed simply for speaking freely."

Hislop has not commented on his decision to resign as an Index patron. However Wheen told the Daily Mail: "His (Coogan's) appointment is a slap in the face.

"Some of the other patrons want Leveson's recommendations to be implemented but the point about Stoppard is that least he does have a long and honourable record of defending freedom of expression elsewhere.

"Whereas Coogan by his own admission, as far as I can see, has never been involved in any such defence of free expression or anything even remotely connected with freedom of speech or the press except for being involved in Hacked Off."